JP2001116908A - Optical sheet and display using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide at low cost a optical sheet which has a sufficient optical function (and durability), specially, a light diffusion sheet (and a display using it) which can be controlled so that high-luminance light with wide wavelength width is scattered and projected as light display light within a predetermined range in a predetermined direction. SOLUTION: Cells composed of brazed type (or binary type) diffraction gratings are arranged in matrix on the top surface of a sheet with light transmissivity and a grating in each cell is formed of a set of curved lines. Here, the sheet is either a light diffusion sheet which has light transmissivity or a reflective light diffusion sheet which has a light reflecting layer formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when applied to various image display devices such as a liquid crystal display device, a plasma display, and a CRT display, improves image quality by increasing brightness, contrast, and viewing area. The present invention relates to an optical sheet suitable for improving the optical sheet. Among the various image display devices described above, a reflection type liquid crystal display device that generates image light (pattern) using ambient light and displays an image is disclosed.
It is particularly suitable for applying the present invention.

[0002]

2. Description of the Related Art The following examples are known as displays to which the above-mentioned optical sheet is applied. (1) Plasma display, CRT display This is a display of a type in which a cell constituting a pixel emits light to generate display light, and a power source for a display light source (an electron gun in the latter case) is required.

(2) Transmissive liquid crystal display device requiring an illumination device such as a backlight A liquid crystal panel is illuminated from the back (the side opposite to the viewer) by an illumination light source such as a backlight or an edge light. A transmissive liquid crystal display device configured to emit a prescribed pattern as display light.

In the above display device, a diffusion sheet, a prism sheet, or the like is used as an optical sheet in order to uniformly irradiate illumination light onto the entire surface of the liquid crystal panel or to control the direction thereof.

(3) Reflective liquid crystal display device that does not require an illumination device such as a backlight A configuration in which a reflector is provided on the back surface of the liquid crystal panel (the side opposite to the viewer), and no special illumination light source is required. In addition, a reflective liquid crystal display device of a type in which reflected light from ambient light (external light such as indoor lighting or sunlight) from the observer side is viewed as patterned display light.

In the above display device, the optical sheet is used as follows in order to control the viewing area of the observer (the area where the display light can be properly viewed). In order to scatter reflected light, which is display light, a diffusion sheet is arranged on the front surface (on the viewer side) of the liquid crystal panel. It is desirable that the diffusion sheet does not diffuse the light incident on the device but diffuses the light reflected and emitted as display light to the observer side. In order to control the reflection direction and the reflection range of the reflected light serving as the display light, a reflector serving as an optical sheet is disposed on the back surface of the liquid crystal panel (the side opposite to the viewer).

It has been attempted to employ a hologram as the above-mentioned reflector in place of an existing scattering reflector (a metal plate having an uneven surface). The following are known as proposals relating to a reflection type liquid crystal display device using a hologram as a reflection plate. (1) JP-A-56-51772 (2) JP-T 8-505716 (3) JP-A-9-152586 (4) JP-A-9-222512 (5) International Publication 96 / 37805

There are various types of holograms, and the characteristics of the reflector change accordingly. In the case of a surface relief hologram, the interference fringes of the hologram (diffusion pattern) are composed of a shallow grating, and the contrast of the fringes is low, making it difficult to increase the diffraction efficiency. Due to the color dispersion of the hologram, the visual color changes according to the viewing direction. This corresponds to (1) above.

In the case of a volume phase reflection type hologram, the wavelength width reflected and diffracted by the wavelength selectivity is narrow and limited (a specific color is obtained), and a bright display pattern over a visible wavelength range is visually recognized. Is difficult. This is
(2) and (3) apply.

In the case of a volume phase transmission type hologram, a bright display pattern over a visible wavelength range can be visually recognized (this is a known matter in the technical field, and detailed description is omitted). Corresponds to (4) and (5) above, but due to the angle selectivity of the volume phase transmission hologram, the reflection layer (reflection plate is composed of a volume phase transmission hologram / reflection layer ) Is difficult to contribute to diffraction (as a result, a bright display pattern is seen).

Further, in common with (2), (3), (4) and (5), in the case of a volume hologram, since the hologram itself is a photosensitive material, the cost is high and there is a problem in durability. .

As the above-mentioned diffusion sheet, a proposal relating to a diffusion sheet using a hologram is also known. The diffusion sheet is produced by photographing and recording a diffusion object such as ground glass on a hologram.

However, when a diffused object is holographically photographed and recorded, when a laser beam is applied to the frosted glass as a subject, a projection pattern (object light) transmitted or reflected by the subject has a random noise called a speckle pattern.

Since the hologram is a recording of a pattern formed by interference between the projection pattern (object light) and the reference light, the contrast of interference fringes recorded due to intensity unevenness due to the speckle pattern is reduced. Would. For this reason, in recording a hologram, it is common practice to improve the diffraction efficiency by using a volume phase hologram represented by a photopolymer.

However, since the volume phase type hologram is itself a photosensitive material, it is vulnerable to environmental changes such as heat and humidity, and because it has a thickness, coloring due to light absorption occurs, and cost is reduced. Would be expensive. (This point is the same as the case of the reflector)

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical sheet having a sufficient optical function (and durability) at low cost. In particular, in a reflection type liquid crystal display device, an optical element that can be controlled so that light having a wide wavelength width and high luminance, which is scattered and reflected to form display light, is emitted as bright display light in a predetermined range and direction. An object is to provide a sheet and a display using the same.

[0017]

In the optical sheet according to the present invention, cells each composed of a diffraction grating are arranged in a matrix on the surface of a light-transmitting sheet, and the lattice in each cell is a collection of curves. It is characterized by comprising.

As the diffraction grating, a blazed diffraction grating or a binary diffraction grating is used instead of a diffraction grating having a low diffraction efficiency unlike a surface relief hologram.

Further, the optical sheet may be applied to a display as a “transmissive light diffusion sheet” while maintaining the translucency, or the optical sheet may be formed with a light reflection layer to form a “reflective light diffusion sheet”. It may be applied as a “sheet”.

<Operation> By employing an optical sheet having a blazed or binary diffraction grating formed thereon, it can be easily embossed on the surface of a thermoplastic resin which is less expensive than a photosensitive material. In addition, an optical sheet having higher diffraction efficiency and higher optical function than the relief hologram can be obtained.

Further, by forming the grid in each cell by a set of curves, it is easy to design each cell to have desired optical characteristics (light diffusion characteristics).

In addition, basically, the optical sheet (light diffusion sheet) of the present invention has no problem in a group of cells made of the same diffraction grating, and it reproduces the diffraction grating cells, which are the minimum structural units, one after another. By doing so, a large-area optical sheet can be manufactured relatively easily.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, as exemplified in FIGS. 1 and 2, an optical system using a diffraction grating array having a fine cell structure and a diffraction grating composed of a collection of curves arranged in a matrix. Adopt a seat. Hereinafter, an optical sheet having a function of generating light diffusion (diffuse transmission or diffuse reflection) will be described.

The size of the cell 11 (21) is about 5 μm to 300 μm because the size of the cell is such that the size of the cell is not recognized when viewed directly and the diffraction effect of the diffraction grating can be sufficiently exhibited. Is desirable.

It is desirable that the depth of the unevenness of the grating is smaller than the wavelength of visible light in order to reduce wavelength selectivity and increase light use efficiency.

Since the diffraction grating in one cell, which is a constituent unit of the diffraction grating array, has only an effect of simply diverging light, its structure is very simple, and it is a shallow surface relief type diffraction grating. Even if this is the case, unlike a hologram having a complicated structure (the grating has a random cross-sectional shape close to a sine wave), the reduction in diffraction efficiency is small.

A blazed diffraction grating is a diffraction grating having a saw-toothed cross-sectional shape. When the angle of reflection or refraction of incident light on the slope is equal to the diffraction angle, a very high diffraction efficiency is obtained. It is known to be obtained.

A binary diffraction grating is a diffraction grating having a step-like cross-sectional shape, and it is known that this diffraction grating also has a very high diffraction efficiency.

In order to sufficiently exhibit the effect of light diffusion by diffraction, it is desirable that the grid lines 12 constituting the diffraction grating are not cut except at the outer periphery of the cell.

When the diffraction grating is illuminated with white light due to the difference in the diffraction angle depending on the wavelength, the diffracted light is dispersed into rainbow colors due to wavelength dispersion.

If the light from the optical sheet undergoes chromatic dispersion and is recognized in different colors by the right and left eyes, the observer feels uncomfortable and causes fatigue. In the case of a display using ambient light, generally, the component of ambient light from above is the largest.
Therefore, it is assumed that light is illuminated from a direction obliquely above the display. At this time, in order to prevent chromatic dispersion from occurring in the left and right eyes, the diffraction grating may have the following relationship.

As shown in FIG. 2, consider a diffraction grating array (optical sheet) formed by a group of cells formed of diffraction gratings formed by translating the same curve in parallel. Needless to say, the grating fringes that make up the diffraction grating are curved
The purpose is to diverge the diffracted light.

FIG. 3 is an explanatory diagram showing an enlarged view of the diffraction grating for one cell in FIG. 2, and is further accompanied by an explanatory diagram showing an enlarged part (right end of the cell).

Here, the interval in the area where the grid pattern is present is d, and the horizontal and vertical components of d are dx and dy. White light is incident on this diffraction grating from above at an angle θ (a perpendicular to the paper is 0 °).

As the diffracted light, light having a wavelength λ has an angle αx in the horizontal (left / right) direction and αy in the vertical (up / down) direction.
In principle, there is a relation of λ = dx * sin (αx) λ = dy * (sin (θ) + sin (αy)). (See Fig. 9)

From the above equation, if the distance dy in the vertical direction is fixed, the light of the wavelength λ will have a constant angular component αy in the vertical direction.
And the light is emitted. Therefore, the vertical grid line spacing d
If y is kept constant, the color in the horizontal direction can be kept constant, and the left and right eyes can observe the display with substantially the same color.

In order to obtain divergent light that spreads to the left and right, a grid whose horizontal angle component αx gradually changes may be used. Therefore, in order to equalize the vertical distance dy between one grid line and another adjacent grid line in any region, the two grid lines must have the same shape, and the two grid lines must have the same shape. Should be fine. If the grid lines are curved,
The distance dx in the x-direction gradually changes, so that diffracted light spreading in the horizontal direction can be obtained.

If such a relationship is applied to all the grating lines constituting the diffraction grating, a diffuser having little change in the color of the diffracted light in the horizontal direction can be obtained. The diffuser based on this diffraction grating has little change in color in the horizontal direction, so it can be recognized with the same color in the left and right eyes, allowing a more natural and less fatigued image to be observed, and changing color in the vertical direction to iridescent. Therefore, it is possible to create a dynamic image with a high eye catching effect.

In some applications, this rainbow color change is not desirable. In this case, the moving distance of the grating line of the diffraction grating is changed. Since this means that dy in the above equation is changed, colors of a plurality of wavelengths are mixed at the viewpoint position, and exhibit a color close to white. At least R,
Since white can be produced by mixing the three colors G and B, it is desirable that the change in the moving distance be three or more.

As described above, according to the present invention, the light diffusing element constituting the light diffusing sheet is not a hologram in which the diffused light is photographed and recorded holographically, but a group of diffractive gratings that generate divergent light. The seat has been realized.

In order to realize a brighter light diffusing sheet with a surface relief type diffraction grating, a blazed grating or a multi-binary diffraction grating having a stepped cross section may be used as the diffraction grating.

In order to realize a bright light diffusion sheet with a small change in color in the horizontal direction using such a blazed grating or a stepwise grating, the following conditions must be satisfied.

It is known that in a blazed grating, when the direction of regular reflection at the slope of the grating coincides with the diffraction angle, strong diffracted light is emitted in the direction of the diffraction angle. In the light diffusion sheet of the present invention, it is required that diffracted light diverge and that the color change in the horizontal direction be small.

For this reason, if the angle component of the blazed slope in the vertical direction is always constant, strong diffracted light will be emitted in this direction. This will be described more specifically with reference to FIG.

FIG. 4 is an explanatory view showing a diffraction grating constituted by translating a curve in the same manner as in FIG.
It is assumed that illumination light is incident on the diffraction grating at an oblique angle of θ. When this diffraction grating is a blazed grating, in order to diffract strong diffracted light toward the front of the display, if the light diffusion sheet by this blazed grating is a reflection type, the slope of the grating line is set at an angle of θ / 2. Just need to be inclined.

Even if the grid line is formed by a curved line, it is sufficient that the vertical angle component of the slope of the grid line always keeps a constant (in this case, θ / 2). . Although the A1-B1 cross section and the A2-B2 cross section in FIG. 4 are cross sections along the moving direction of the grid lines, the angle of the slope of the blazed grid in these two cross sections is constant.

FIG. 5 is an explanatory view showing a binary diffraction grating whose depth changes stepwise. Even when the grid lines are configured in a stepped manner, if the vertical angle component of the grid line slope always maintains a constant (in this case, θ / 2) relationship, strong diffraction occurs in front of the display. Light can be diffracted. Therefore, as shown in FIG. 5, the cross section obtained by cutting the stepwise grid in the vertical direction may be the same at any position of the grid line.

FIG. 6 is an explanatory diagram showing an example of the configuration of a display to which the optical sheet (light diffusion sheet) of the present invention is applied. The light diffusion sheet shown in the figure has a function as a “reflection sheet” in which a light reflection layer is formed on the surface of a diffraction grating by vapor deposition, sputtering, or the like, and is opposite to a viewer on the image display surface. It is explanatory drawing which concerns on the "reflection type" display which arranges the said light-diffusion sheet on the side. After the illumination light 31 is diffusely reflected by the light diffusion sheet 35, the illumination light 31 passes through the polarizing plate 37, the liquid crystal layer 38, and the polarizing plate 37, so that the display pattern 32 can be viewed by an observer.

In the case of a display utilizing ambient environment light, such as a reflection type liquid crystal display device which does not require a special light source, the illumination light 31 is generally illuminated obliquely from above as shown in FIG. When the light diffusion sheet 35 is based on a blazed grating or a step-like grating, its slope is
It is desirable to face the top (up) direction of the display.

FIG. 6 illustrates the case of a reflection type liquid crystal display device using ambient light, but the display is not limited to the "reflection type", and the display light is obtained by reflecting edge light. Applicable to types of displays. In addition, without forming a light reflection layer on the optical sheet (light diffusion sheet), while maintaining the translucency,
A “transmission type display” to which a “transmission sheet” is applied may be used.

In the case of a transmissive display, an optical sheet (light diffusion sheet) is arranged on the viewer side of the image display surface so that display light is emitted in a predetermined range and direction.
Taking a liquid crystal display device as an example, in FIG. 6, the optical sheet (light diffusion sheet) 35 is disposed on the right side of the liquid crystal layer 38.

In recent years, in a liquid crystal display device, a technique for improving the aperture ratio of a liquid crystal cell by using a lower drive electrode (opposite to a viewer) as a reflective layer (hereinafter referred to as a reflective electrode) has been developed. Has appeared.

The reflective electrode has a mirror surface or minute circular irregularities formed on the surface. In the case of a mirror surface, since there is no diffusion at the electrode, it is necessary to widen the range (viewing area) from which display light is emitted by other components. If minute circular irregularities are formed on the surface, Diffusivity is insufficient and control of the degree of diffusion is difficult.

Therefore, it is effective to apply the optical sheet (light diffusion sheet) of the present invention to a liquid crystal display device having a reflective electrode. On the reflective surface of the reflective electrode or on it,
By arranging a light diffusing sheet composed of a group of divergent diffraction grating cells, light can be efficiently diffused.

Since the diffraction grating has a different diffraction angle (wavelength dispersion) depending on the wavelength, when near-white light is required, it can be realized by changing the period of the diffraction grating within a relatively narrow region. That is, by mixing the diffracted lights having different wavelengths, the influence of the wavelength dispersion can be avoided, and the diffracted light close to white can be obtained. Alternatively, even if the angle of diffraction by the diffraction grating is reduced, it is possible to reduce the problem of coloring and obtain diffracted light close to white.

If the reflective electrode is sufficiently small having a size of 0.3 mm or less, there is no need to provide a plurality of diffraction grating cells in each electrode. One electrode corresponds to one electrode, and the electrode ( Even if a diffraction grating array is formed as a collection of diffraction grating cells, the effect of the present invention is not impaired.

When a diffraction grating array (light diffusion sheet) is formed by a group of diffraction grating cells having an effect of diverging light, a grid line forming the diffraction grating is cut off at a boundary between cells, and a portion thereof is formed. In this case, the power for controlling light by diffraction is reduced.

As typified by a liquid crystal display device, most displays have a pixel structure, and there are many cases where a gap exists between pixels. In the case of a liquid crystal display, a non-pixel black matrix around the liquid crystal cell is a prominent example. By arranging an optical sheet having a blazed (or binary) diffraction grating cell as a constituent unit on an image display surface displaying an image in pixel units in such a manner that the cell-shaped diffraction grating corresponds to the pixel, The light from the pixel can be made to function efficiently, and in particular, it is possible to prevent a reduction in light control ability due to diffraction at the boundary region of the diffraction grating cell.

In order to accurately form a blazed or binary diffraction grating having a curved line as in the present invention, a patterning apparatus used in a semiconductor manufacturing process is used. In the apparatus, a pattern is formed by focusing and scanning an electron beam or a laser beam.

FIG. 7 conceptually shows a method of performing writing while controlling the depth of the grating by changing the amount of energy for each region to be irradiated with the electron beam when writing the blazed grating by the electron beam. FIG. In the figure, the thickness of the arrow indicates the amount of energy, and a lattice is formed deep in a region where the amount of energy is large.

As a method of modulating the irradiation intensity of the electron beam, a method of directly controlling a dose amount, a method of changing a scanning speed (time), and a method of scanning the same portion a plurality of times are described.
There is a method of changing the number of scans. The above description is also applicable to the step-like binary grating.

Further, a method other than drawing by an electron beam or a laser beam can be adopted. FIG. 8 is an explanatory view conceptually showing a method of forming a four-stage binary lattice by etching with an ion beam.

In the figure, etching using two types of mask patterns is performed. In FIG. 8A, using a first mask pattern, the photosensitive material is selectively etched by an ion beam that has passed through an opening of the mask.

A rectangular concave portion as shown in FIG. B is formed in the photosensitive material. Next, as shown in FIG. 4C, the photosensitive material is selectively etched by the ion beam passing through the opening of the mask using the second mask pattern, and finally, as shown in FIG. A rectangular recess will be formed.

In the above process, by increasing the number of mask patterns and the number of times of etching, it is possible to form a binary type lattice having further increased stages.

As described above, after the photosensitive material having the diffraction grating of the desired shape formed on the surface is developed to obtain an original plate,
A stamper (duplication plate) in which the diffraction grating of the original plate is reproduced based on the original plate by plating or the like is obtained, and the stamper facilitates large-scale duplication of the diffraction grating by embossing the thermoplastic resin sheet.

As described above, the cost can be reduced by forming the optical sheet with a thermoplastic resin sheet. However, in the case of embossing the thermoplastic resin sheet,
There is a limit in forming a fine diffraction grating with high precision, and in order to further form a fine diffraction grating with high precision, it is preferable to use a photosensitive resin (photocurable resin).

[0068]

According to the present invention, an optical sheet having a high diffraction efficiency and exhibiting a sufficient optical function (and durability) can be provided at low cost. Also, by changing the shape, pitch, depth, etc. of the diffraction grating for each region of the optical sheet, it is possible to change the optical function for each region, so that one optical sheet has a plurality of functions. The number of optical members can be reduced, and the cost of the display device can be further reduced.

[0069]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of an optical sheet (light diffusion sheet) according to the present invention, in which a cell composed of a diffraction grating formed by a collection of curves having different curvatures is used as a constituent unit.

FIG. 2 is an explanatory diagram showing a diffraction grating array (optical sheet) formed by a group of cells formed of diffraction gratings formed by translating the same curve in parallel.

FIG. 3 is an explanatory diagram showing an enlarged diffraction grating for one cell in FIG. 2;

FIG. 4 is an explanatory view showing a diffraction grating having a blazed cross section, which is formed by moving a curve in parallel.

FIG. 5 is an explanatory view showing a binary diffraction grating whose depth changes stepwise.

FIG. 6 is an explanatory view showing an example of the configuration of a display to which the optical sheet (light diffusion sheet) of the present invention is applied.

FIG. 7 is an explanatory view conceptually showing a method of performing writing while controlling the depth of the grating by changing the amount of energy for each region irradiated with the electron beam when writing a blazed grating by an electron beam.

FIG. 8 is an explanatory view conceptually showing a method for forming a four-stage binary lattice by etching with an ion beam.

FIG. 9 is an explanatory diagram showing a relationship between incident light and output light (diffraction light) with respect to the diffraction grating.

[Explanation of symbols]

 11, 21… Diffraction grating cell 12… Grating line 31… Illumination light 32… Display pattern 35… Light diffusion sheet 37… Polarizing plate 38… Liquid crystal layer

Claims (16)

[Claims] 1. An optical sheet having a light-transmitting sheet whose surface constitutes a blazed diffraction grating, wherein cells composed of the blazed diffraction grating are arranged in a matrix on the sheet surface. An optical sheet, wherein the inner grating is constituted by a collection of curves. 2. The optical sheet according to claim 1, further comprising a cell formed of a diffraction grating formed by translating the same curve in parallel. 3. The optical sheet according to claim 1, further comprising a cell formed of a diffraction grating formed by a collection of curves having different curvatures. 4. A cell comprising a diffraction grating having at least three types of pitches.
The optical sheet according to any one of the above. 5. The optical sheet according to claim 1, wherein the angle of the slope of the blazed diffraction grating is constant within the same cell in the moving direction of the curve. 6. An optical sheet in which the surface of a sheet having translucency constitutes a binary diffraction grating having a stepwise-depth-changed depth, wherein cells comprising the binary diffraction grating are arranged in a matrix on the sheet surface. Wherein the grating in each cell is constituted by a collection of curves. 7. The optical sheet according to claim 6, wherein the same sheet includes a cell formed of a diffraction grating formed by translation. 8. The optical sheet according to claim 6, comprising a cell composed of a diffraction grating formed by a collection of curves having different curvatures. 9. A cell comprising a diffraction grating having at least three types of pitches.
The optical sheet according to any one of the above. 10. The angle of the slope of the binary diffraction grating is:
The optical sheet according to any one of claims 6 to 9, wherein the moving direction of the curve is constant within the same cell. 11. The optical sheet according to claim 1, wherein a light reflection layer is formed on the surface of the diffraction grating by vapor deposition, sputtering, or the like. 12. The image display device according to claim 1, wherein:
0. A display having a configuration in which the optical sheet according to any one of 0 is arranged. 13. A display having a structure in which the optical sheet according to claim 11 is arranged on a side of an image display surface opposite to a viewer. 14. An optical sheet according to any one of claims 1 to 10, wherein a cell comprising a diffraction grating and said pixel are arranged on an observer side of an image display surface for displaying an image in pixel units. A display with a configuration. 15. The image display device according to claim 12, wherein the slope of the diffraction grating faces upward (upward) on the image display surface.
Or the display according to 13. 16. An optical sheet according to any one of claims 1 to 10, wherein an arrangement pitch of cells comprising a diffraction grating is arranged on a viewer side of an image display surface for displaying an image in pixel units. A display configured to correspond to an integer multiple of.